Liverpool were embroiled in a fresh racism controversy night, after the Oldham Athletic defender Tom Adeyemi alleged that he was racially abused twice by a supporter during an FA Cup tie at Anfield.

The incident occurred 10 minutes from the end of Liverpool's 5-1 win over the League One side. The 20-year-old Adeyemi, who is on loan from Norwich City, became involved in an altercation with a supporter, or supporters, at the front of the Kop. Before leaving the stadium Adeyemi gave a statement to Merseyside Police in which it is understood he claimed to have been racially abused twice by a supporter.

Adeyemi was visibly upset by the exchange and it required several team-mates, the Liverpool captain, Steven Gerrard, and the referee, Neil Swarbrick, to calm him down. He was booked seconds later for a wild foul on the Liverpool substitute John Flanagan.

Witnesses reported seeing two fans wearing Luis Suárez T-shirts – similar to those worn by Liverpool players at Wigan last month, after the Uruguayan was found guilty of racially abusing Patrice Evra – confronting Adeyemi. A witness who gave evidence to Liverpool officials and the police said: "I was to the right of the Kop and the No11 turned to walk away after a tackle. I heard a single voice shout, 'You fucking black bastard.' He spun round with shock on his face and started pointing at the crowd, from where the shout had come."

Merseyside police said that arrests were made at the game but not in relation to the alleged abuse of Adeyemi. A statement said: "Merseyside police can confirm that no one has been arrested this evening on suspicion of racially aggravated behaviour during tonight's FA Cup fixture at Anfield. However, the force and Liverpool Football Club are investigating following an incident that occurred during the second half of the game. The aim of the investigation is to establish the full circumstances surrounding the incident to ascertain if any action needs to be taken."

Liverpool launched an investigation into an incident that could not have come at a worse time for a club that has been widely condemned for its vehement support of Suárez, before and after his eight-match ban for racially abusing Evra in a match last October.

The Liverpool manager, Kenny Dalglish, was not able to comment. He gave his post-match press conference shortly after the final whistle. But a Liverpool statement said: "An incident occurred in the second half of the match which is now being investigated by both the club and the police. We will continue to work closely with the police to establish the details of what actually happened and will make a further statement in due course."

The Oldham Athletic manager, Paul Dickov, said Adeyemi was calm in the dressing room after the game but said that the player's on-field response to the alleged abuse had been out of character.

"From my point of view I have not spoken to Tom but something has been said," Dickov said. "He is a placid boy and well-educated lad with a fantastic temperament. He never raises his voice so for him to react like that, something has been said but what that is I don't know. I have not heard. I've just been told the police are investigating it.

"I haven't spoken to him directly about what happened because I was in the dressing room telling all the lads how proud I was of their performance. He is fine now. He has calmed down. He is a laid-back character. Our players and the Liverpool players helped calm him down, which showed they are fantastic professionals."